SharePoint sometimes has separate language packs for several variants of closely related languages, like Brazilian and European Portuguese, or several varieties in the Serbo-Croatian family of languages. In other cases, you have to live with a different variant of your language, so for instance people in the UK must use the American flavo
r of English with American spelling and vocabulary, and Flemish-speaking Belgians must use Dutch, with all its differences in vocabulary
For Persian, the language spoken in Iran, there is no direct support. However in SharePoint 2013 and 2016 and in SharePoint Online, you do have the option of selecting Dari. Dari is a language of Afghanistan, the native language of about 20% of the population. It is also known as Dari Persian, Afghan Persian, and simply Farsi. Although the spoken version sounds quite different from Iranian Persian spoken in Tehran, the written language is nearly the same. Download the SharePoint Dari Language Pack
and use it instead of Persian.
For languages where SharePoint supports a slightly different version of the language that you want, PointFire
gives you the option in a lot of cases to override specific text from SharePoint's language packs and use your different text instead.
SharePoint has a machine translation service that can be used to translate certain documents and phrases. Out of the box, it can be used by Variations to translate pages, and by the Managed Metadata Service to translate terms in the term stores. Beyond that, it is available through the API, and PointFire products make use of it.
For the past several months, Microsoft has been introducing a far superior machine translation engine. So far it is available in English, French, Arabic, Chinese simplified (Mandarin), German, Italian, Japanese, Korean, Portuguese, Russian, and Spanish.
It is not automatically used unless you specifically configure the machine translation service for it. Simply open a session in the SharePoint Management Shell and issue this commandlet:
Set-SPTranslationServiceApplication "Machine Translation Service" -MachineTranslationCategory generalnn
That's it! In this case the service was named "Machine Translation Service". For examples of the old vs the new engine, see http://translate.ai
SharePoint Online uses the old engine, and there is nothing you can do about it. I don't think you can configure the machine translation service for your tenant. Maybe you can request it nicely or vote it up